A transistor is an electronic device that permits current flow in electronic circuits. In this regard, the transistor permits the current to flow in a controlled manner whenever an electronic circuit attempts to push current through the transistor. In this manner, the transistor generically operates as a regulator or valve, which regulates the flow of current.
FIG. 1 illustrates an exemplary conventional complementary metal oxide semiconductor (CMOS) transistor arrangement. Referring to FIG. 1, the conventional CMOS transistor arrangement 24 includes an n-channel MOS (NMOS) transistor 18 and a p-channel MOS (PMOS) transistor 20. The conventional CMOS arrangement 24 also includes a p-substrate 14, for example a p−-substrate. The NMOS transistor 18 is disposed within the p-substrate 14. The NMOS transistor 18 includes a p+-body contact (B), an n+-source (S) and an n+-drain (D) disposed in the p-substrate 14. A voltage source VSS 6 having a ground is coupled to the p+-body contact (B) and the voltage source VSS 4 is coupled to the n+-source (S) of NMOS transistor 18. An input line 2 is coupled to a gate (G) of the NMOS transistor 18. An output line 10 is coupled to the n+-drain (D) of the NMOS transistor 18. The PMOS transistor 20 includes an n-well 22 that is disposed in the p-substrate 14. The PMOS transistor 20 also includes an n+-body contact (B), a p+-source (S) and a p+-drain (D) disposed in the n-well 22. A voltage source VDD 8 is coupled to the p+-source (S) and the n+-body contact (B) of PMOS transistor 22. The input line 2 is also coupled to a gate of the PMOS transistor 20. The output line 10 is also coupled to the p+-drain (D) of the PMOS transistor 20.
During normal operation of the conventional CMOS transistor arrangement 24, the voltage sources VSS 4, VDD 8 may be noisy. For example, the noise may be caused by other circuitry found on or coupled to the chip that may directly or indirectly affect the voltage sources VSS 4, VDD 8. High swing or high power devices such as, data drivers in a wire line communication system or transmitters in wireless communications systems, may be sources of noise. The noise may also be caused, for example, by the driving of active circuits. In one example, the voltage sources may be coupled to active circuitry such as active portions of an inverter circuit, which may cause transient currents to flow during signal transitions from a high level to a low level or from a low level to a high level. In another example, noise may be caused by transitions in a signal propagated or generated by the chip.
In the NMOS transistor 18, if the voltage source VSS 4, VSS 6 is noisy, then the noise may propagate to the p-substrate 14 via, for example, at least through the resistive coupling 9 between the p+-body contact (B) and the p-substrate 14. In the PMOS transistor 20, if the voltage source VDD 8 is noisy, then the noise may propagate to the n-well 22 via the n+-body contact (B) of the PMOS transistor 20 via a resistive coupling 12. The noise in the n-well 22 may propagate to the p-substrate 14 via, for example, at least the capacitive coupling 16 between the n-well 22 and the p-substrate 14. If the noise is able to propagate to the p-substrate 14, then noise may propagate to or otherwise affect other circuits on or off the chip that may be coupled to the p-substrate 14.
In order to mitigate the effects of impairments such as noise, transistors may be arranged so that they form a differential amplifier. Differential amplifiers form the basis of operational amplifiers, the latter of which are generally referred to as op amps. Differential amplifiers are electronic circuits, which are designed with an internal symmetry that is configured to cancel errors which are shared by both sides of the differential amplifier. These errors may include internal or external errors. Internal errors may include temperature changes, which in certain instances, may affect both sides of the operational amplifier to approximately the same degree. Transistor mismatch is another example of an internal error. Whenever both sides are affected to approximately the same degree, a nulling or canceling effect occurs. External errors may include noise picked up by inputs of the differential amplifier. In this regard, the differential amplifier may be adapted to eliminate common mode noise. Furthermore, the differential amplifier may require that the signal appear as a difference between waveforms occurring on either side of the differential amplifier. Accordingly, the differential amplifier may be configured to reject certain signal components such as noise and amplify desired signal components.
Some conventional differential amplifiers require a reference voltage or reference current in order for the differential amplifier to operate properly. Additionally, some differential amplifier designs utilize large numbers of transistors. In general, the greater the number of transistor devices, the greater the number of operating variables that will vary with respect to each of the sides of a differential amplifier. Consequently, differential amplifiers that utilize a large number of transistors may be more difficult to control and tune, and may also be less predictable with respect to process or operating variations. Furthermore, most conventional analog differential amplifiers are generally adapted to take a relatively small differential input voltage and produce as an output a voltage having a larger magnitude. These conventional analog differential amplifiers are usually optimized to operate in a specified voltage range and may not function at all if operated outside that range.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.